diff --git a/packages/opencode/src/control-plane/workspace.ts b/packages/opencode/src/control-plane/workspace.ts
index e825eaddcf..00353dcca3 100644
--- a/packages/opencode/src/control-plane/workspace.ts
+++ b/packages/opencode/src/control-plane/workspace.ts
@@ -676,14 +676,12 @@ export const layer = Layer.effect(
         }
 
         if (input.workspaceID === null) {
-          yield* Effect.sync(() =>
-            SyncEvent.run(Session.Event.Updated, {
-              sessionID: input.sessionID,
-              info: {
-                workspaceID: null,
-              },
-            }),
-          )
+          yield* sync.run(Session.Event.Updated, {
+            sessionID: input.sessionID,
+            info: {
+              workspaceID: null,
+            },
+          })
 
           log.info("session warp complete", {
             workspaceID: input.workspaceID,
diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
index 3b16a9a5d7..4eafbdf749 100644
--- a/packages/opencode/src/session/compaction.ts
+++ b/packages/opencode/src/session/compaction.ts
@@ -18,8 +18,9 @@ import { InstanceState } from "@/effect/instance-state"
 import { isOverflow as overflow, usable } from "./overflow"
 import { makeRuntime } from "@/effect/run-service"
 import { serviceUse } from "@/effect/service-use"
-import { EventV2 } from "@/v2/event"
+import { SyncEvent } from "@/sync"
 import { SessionEvent } from "@/v2/session-event"
+import { Flag } from "@opencode-ai/core/flag/flag"
 
 const log = Log.create({ service: "session.compaction" })
 
@@ -219,6 +220,7 @@ export const layer: Layer.Layer<
   | Plugin.Service
   | SessionProcessor.Service
   | Provider.Service
+  | SyncEvent.Service
 > = Layer.effect(
   Service,
   Effect.gen(function* () {
@@ -229,6 +231,7 @@ export const layer: Layer.Layer<
     const plugin = yield* Plugin.Service
     const processors = yield* SessionProcessor.Service
     const provider = yield* Provider.Service
+    const sync = yield* SyncEvent.Service
 
     const isOverflow = Effect.fn("SessionCompaction.isOverflow")(function* (input: {
       tokens: MessageV2.Assistant["tokens"]
@@ -567,12 +570,14 @@ export const layer: Layer.Layer<
             parts: [],
           },
         )
-        EventV2.run(SessionEvent.Compaction.Ended.Sync, {
-          sessionID: input.sessionID,
-          timestamp: DateTime.makeUnsafe(Date.now()),
-          text: summary ?? "",
-          include: selected.tail_start_id,
-        })
+        if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+          yield* sync.run(SessionEvent.Compaction.Ended.Sync, {
+            sessionID: input.sessionID,
+            timestamp: DateTime.makeUnsafe(Date.now()),
+            text: summary ?? "",
+            include: selected.tail_start_id,
+          })
+        }
         yield* bus.publish(Event.Compacted, { sessionID: input.sessionID })
       }
       return result
@@ -601,11 +606,13 @@ export const layer: Layer.Layer<
         auto: input.auto,
         overflow: input.overflow,
       })
-      EventV2.run(SessionEvent.Compaction.Started.Sync, {
-        sessionID: input.sessionID,
-        timestamp: DateTime.makeUnsafe(Date.now()),
-        reason: input.auto ? "auto" : "manual",
-      })
+      if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+        yield* sync.run(SessionEvent.Compaction.Started.Sync, {
+          sessionID: input.sessionID,
+          timestamp: DateTime.makeUnsafe(Date.now()),
+          reason: input.auto ? "auto" : "manual",
+        })
+      }
     })
 
     return Service.of({
@@ -626,6 +633,7 @@ export const defaultLayer = Layer.suspend(() =>
     Layer.provide(Plugin.defaultLayer),
     Layer.provide(Bus.layer),
     Layer.provide(Config.defaultLayer),
+    Layer.provide(SyncEvent.defaultLayer),
   ),
 )
 
diff --git a/packages/opencode/src/session/processor.ts b/packages/opencode/src/session/processor.ts
index 7df54d5451..579c4cc42c 100644
--- a/packages/opencode/src/session/processor.ts
+++ b/packages/opencode/src/session/processor.ts
@@ -21,10 +21,11 @@ import { Question } from "@/question"
 import { errorMessage } from "@/util/error"
 import * as Log from "@opencode-ai/core/util/log"
 import { isRecord } from "@/util/record"
-import { EventV2 } from "@/v2/event"
+import { SyncEvent } from "@/sync"
 import { SessionEvent } from "@/v2/session-event"
 import { Modelv2 } from "@/v2/model"
 import * as DateTime from "effect/DateTime"
+import { Flag } from "@opencode-ai/core/flag/flag"
 
 const DOOM_LOOP_THRESHOLD = 3
 const log = Log.create({ service: "session.processor" })
@@ -96,6 +97,7 @@ export const layer: Layer.Layer<
   | Image.Service
   | SessionSummary.Service
   | SessionStatus.Service
+  | SyncEvent.Service
 > = Layer.effect(
   Service,
   Effect.gen(function* () {
@@ -111,6 +113,7 @@ export const layer: Layer.Layer<
     const scope = yield* Scope.Scope
     const status = yield* SessionStatus.Service
     const image = yield* Image.Service
+    const sync = yield* SyncEvent.Service
 
     const create = Effect.fn("SessionProcessor.create")(function* (input: Input) {
       // Pre-capture snapshot before the LLM stream starts. The AI SDK
@@ -229,11 +232,13 @@ export const layer: Layer.Layer<
           case "reasoning-start":
             if (value.id in ctx.reasoningMap) return
             // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-            EventV2.run(SessionEvent.Reasoning.Started.Sync, {
-              sessionID: ctx.sessionID,
-              reasoningID: value.id,
-              timestamp: DateTime.makeUnsafe(Date.now()),
-            })
+            if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+              yield* sync.run(SessionEvent.Reasoning.Started.Sync, {
+                sessionID: ctx.sessionID,
+                reasoningID: value.id,
+                timestamp: DateTime.makeUnsafe(Date.now()),
+              })
+            }
             ctx.reasoningMap[value.id] = {
               id: PartID.ascending(),
               messageID: ctx.assistantMessage.id,
@@ -262,12 +267,14 @@ export const layer: Layer.Layer<
           case "reasoning-end":
             if (!(value.id in ctx.reasoningMap)) return
             // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-            EventV2.run(SessionEvent.Reasoning.Ended.Sync, {
-              sessionID: ctx.sessionID,
-              reasoningID: value.id,
-              text: ctx.reasoningMap[value.id].text,
-              timestamp: DateTime.makeUnsafe(Date.now()),
-            })
+            if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+              yield* sync.run(SessionEvent.Reasoning.Ended.Sync, {
+                sessionID: ctx.sessionID,
+                reasoningID: value.id,
+                text: ctx.reasoningMap[value.id].text,
+                timestamp: DateTime.makeUnsafe(Date.now()),
+              })
+            }
             // oxlint-disable-next-line no-self-assign -- reactivity trigger
             ctx.reasoningMap[value.id].text = ctx.reasoningMap[value.id].text
             ctx.reasoningMap[value.id].time = { ...ctx.reasoningMap[value.id].time, end: Date.now() }
@@ -281,12 +288,14 @@ export const layer: Layer.Layer<
               throw new Error(`Tool call not allowed while generating summary: ${value.toolName}`)
             }
             // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-            EventV2.run(SessionEvent.Tool.Input.Started.Sync, {
-              sessionID: ctx.sessionID,
-              callID: value.id,
-              name: value.toolName,
-              timestamp: DateTime.makeUnsafe(Date.now()),
-            })
+            if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+              yield* sync.run(SessionEvent.Tool.Input.Started.Sync, {
+                sessionID: ctx.sessionID,
+                callID: value.id,
+                name: value.toolName,
+                timestamp: DateTime.makeUnsafe(Date.now()),
+              })
+            }
             const part = yield* session.updatePart({
               id: ctx.toolcalls[value.id]?.partID ?? PartID.ascending(),
               messageID: ctx.assistantMessage.id,
@@ -310,12 +319,14 @@ export const layer: Layer.Layer<
 
           case "tool-input-end": {
             // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-            EventV2.run(SessionEvent.Tool.Input.Ended.Sync, {
-              sessionID: ctx.sessionID,
-              callID: value.id,
-              text: "",
-              timestamp: DateTime.makeUnsafe(Date.now()),
-            })
+            if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+              yield* sync.run(SessionEvent.Tool.Input.Ended.Sync, {
+                sessionID: ctx.sessionID,
+                callID: value.id,
+                text: "",
+                timestamp: DateTime.makeUnsafe(Date.now()),
+              })
+            }
             return
           }
 
@@ -325,17 +336,19 @@ export const layer: Layer.Layer<
             }
             const toolCall = yield* readToolCall(value.toolCallId)
             // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-            EventV2.run(SessionEvent.Tool.Called.Sync, {
-              sessionID: ctx.sessionID,
-              callID: value.toolCallId,
-              tool: value.toolName,
-              input: value.input,
-              provider: {
-                executed: toolCall?.part.metadata?.providerExecuted === true,
-                ...(value.providerMetadata ? { metadata: value.providerMetadata } : {}),
-              },
-              timestamp: DateTime.makeUnsafe(Date.now()),
-            })
+            if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+              yield* sync.run(SessionEvent.Tool.Called.Sync, {
+                sessionID: ctx.sessionID,
+                callID: value.toolCallId,
+                tool: value.toolName,
+                input: value.input,
+                provider: {
+                  executed: toolCall?.part.metadata?.providerExecuted === true,
+                  ...(value.providerMetadata ? { metadata: value.providerMetadata } : {}),
+                },
+                timestamp: DateTime.makeUnsafe(Date.now()),
+              })
+            }
             yield* updateToolCall(value.toolCallId, (match) => ({
               ...match,
               tool: value.toolName,
@@ -405,27 +418,29 @@ export const layer: Layer.Layer<
               attachments: attachments?.length ? attachments : undefined,
             }
             // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-            EventV2.run(SessionEvent.Tool.Success.Sync, {
-              sessionID: ctx.sessionID,
-              callID: value.toolCallId,
-              structured: output.metadata,
-              content: [
-                {
-                  type: "text",
-                  text: output.output,
+            if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+              yield* sync.run(SessionEvent.Tool.Success.Sync, {
+                sessionID: ctx.sessionID,
+                callID: value.toolCallId,
+                structured: output.metadata,
+                content: [
+                  {
+                    type: "text",
+                    text: output.output,
+                  },
+                  ...(output.attachments?.map((item: MessageV2.FilePart) => ({
+                    type: "file",
+                    uri: item.url,
+                    mime: item.mime,
+                    name: item.filename,
+                  })) ?? []),
+                ],
+                provider: {
+                  executed: toolCall?.part.metadata?.providerExecuted === true,
                 },
-                ...(output.attachments?.map((item: MessageV2.FilePart) => ({
-                  type: "file",
-                  uri: item.url,
-                  mime: item.mime,
-                  name: item.filename,
-                })) ?? []),
-              ],
-              provider: {
-                executed: toolCall?.part.metadata?.providerExecuted === true,
-              },
-              timestamp: DateTime.makeUnsafe(Date.now()),
-            })
+                timestamp: DateTime.makeUnsafe(Date.now()),
+              })
+            }
             yield* completeToolCall(value.toolCallId, output)
             return
           }
@@ -433,18 +448,20 @@ export const layer: Layer.Layer<
           case "tool-error": {
             const toolCall = yield* readToolCall(value.toolCallId)
             // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-            EventV2.run(SessionEvent.Tool.Failed.Sync, {
-              sessionID: ctx.sessionID,
-              callID: value.toolCallId,
-              error: {
-                type: "unknown",
-                message: errorMessage(value.error),
-              },
-              provider: {
-                executed: toolCall?.part.metadata?.providerExecuted === true,
-              },
-              timestamp: DateTime.makeUnsafe(Date.now()),
-            })
+            if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+              yield* sync.run(SessionEvent.Tool.Failed.Sync, {
+                sessionID: ctx.sessionID,
+                callID: value.toolCallId,
+                error: {
+                  type: "unknown",
+                  message: errorMessage(value.error),
+                },
+                provider: {
+                  executed: toolCall?.part.metadata?.providerExecuted === true,
+                },
+                timestamp: DateTime.makeUnsafe(Date.now()),
+              })
+            }
             yield* failToolCall(value.toolCallId, value.error)
             return
           }
@@ -456,17 +473,19 @@ export const layer: Layer.Layer<
             if (!ctx.snapshot) ctx.snapshot = yield* snapshot.track()
             if (!ctx.assistantMessage.summary) {
               // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-              EventV2.run(SessionEvent.Step.Started.Sync, {
-                sessionID: ctx.sessionID,
-                agent: input.assistantMessage.agent,
-                model: {
-                  id: Modelv2.ID.make(ctx.model.id),
-                  providerID: Modelv2.ProviderID.make(ctx.model.providerID),
-                  variant: Modelv2.VariantID.make(input.assistantMessage.variant ?? "default"),
-                },
-                snapshot: ctx.snapshot,
-                timestamp: DateTime.makeUnsafe(Date.now()),
-              })
+              if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+                yield* sync.run(SessionEvent.Step.Started.Sync, {
+                  sessionID: ctx.sessionID,
+                  agent: input.assistantMessage.agent,
+                  model: {
+                    id: Modelv2.ID.make(ctx.model.id),
+                    providerID: Modelv2.ProviderID.make(ctx.model.providerID),
+                    variant: Modelv2.VariantID.make(input.assistantMessage.variant ?? "default"),
+                  },
+                  snapshot: ctx.snapshot,
+                  timestamp: DateTime.makeUnsafe(Date.now()),
+                })
+              }
             }
             yield* session.updatePart({
               id: PartID.ascending(),
@@ -486,14 +505,16 @@ export const layer: Layer.Layer<
             })
             if (!ctx.assistantMessage.summary) {
               // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-              EventV2.run(SessionEvent.Step.Ended.Sync, {
-                sessionID: ctx.sessionID,
-                finish: value.finishReason,
-                cost: usage.cost,
-                tokens: usage.tokens,
-                snapshot: completedSnapshot,
-                timestamp: DateTime.makeUnsafe(Date.now()),
-              })
+              if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+                yield* sync.run(SessionEvent.Step.Ended.Sync, {
+                  sessionID: ctx.sessionID,
+                  finish: value.finishReason,
+                  cost: usage.cost,
+                  tokens: usage.tokens,
+                  snapshot: completedSnapshot,
+                  timestamp: DateTime.makeUnsafe(Date.now()),
+                })
+              }
             }
             ctx.assistantMessage.finish = value.finishReason
             ctx.assistantMessage.cost += usage.cost
@@ -541,10 +562,12 @@ export const layer: Layer.Layer<
           case "text-start":
             if (!ctx.assistantMessage.summary) {
               // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-              EventV2.run(SessionEvent.Text.Started.Sync, {
-                sessionID: ctx.sessionID,
-                timestamp: DateTime.makeUnsafe(Date.now()),
-              })
+              if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+                yield* sync.run(SessionEvent.Text.Started.Sync, {
+                  sessionID: ctx.sessionID,
+                  timestamp: DateTime.makeUnsafe(Date.now()),
+                })
+              }
             }
             ctx.currentText = {
               id: PartID.ascending(),
@@ -586,11 +609,13 @@ export const layer: Layer.Layer<
             )).text
             if (!ctx.assistantMessage.summary) {
               // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-              EventV2.run(SessionEvent.Text.Ended.Sync, {
-                sessionID: ctx.sessionID,
-                text: ctx.currentText.text,
-                timestamp: DateTime.makeUnsafe(Date.now()),
-              })
+              if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+                yield* sync.run(SessionEvent.Text.Ended.Sync, {
+                  sessionID: ctx.sessionID,
+                  text: ctx.currentText.text,
+                  timestamp: DateTime.makeUnsafe(Date.now()),
+                })
+              }
             }
             {
               const end = Date.now()
@@ -680,14 +705,16 @@ export const layer: Layer.Layer<
         }
         if (!ctx.assistantMessage.summary) {
           // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-          EventV2.run(SessionEvent.Step.Failed.Sync, {
-            sessionID: ctx.sessionID,
-            error: {
-              type: "unknown",
-              message: errorMessage(e),
-            },
-            timestamp: DateTime.makeUnsafe(Date.now()),
-          })
+          if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+            yield* sync.run(SessionEvent.Step.Failed.Sync, {
+              sessionID: ctx.sessionID,
+              error: {
+                type: "unknown",
+                message: errorMessage(e),
+              },
+              timestamp: DateTime.makeUnsafe(Date.now()),
+            })
+          }
         }
         ctx.assistantMessage.error = error
         yield* bus.publish(Session.Event.Error, {
@@ -732,22 +759,28 @@ export const layer: Layer.Layer<
                 parse,
                 set: (info) => {
                   // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-                  EventV2.run(SessionEvent.Retried.Sync, {
-                    sessionID: ctx.sessionID,
-                    attempt: info.attempt,
-                    error: {
-                      message: info.message,
-                      isRetryable: true,
-                    },
-                    timestamp: DateTime.makeUnsafe(Date.now()),
-                  })
-                  return status.set(ctx.sessionID, {
-                    type: "retry",
-                    attempt: info.attempt,
-                    message: info.message,
-                    action: info.action,
-                    next: info.next,
-                  })
+                  const event = Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM
+                    ? sync.run(SessionEvent.Retried.Sync, {
+                        sessionID: ctx.sessionID,
+                        attempt: info.attempt,
+                        error: {
+                          message: info.message,
+                          isRetryable: true,
+                        },
+                        timestamp: DateTime.makeUnsafe(Date.now()),
+                      })
+                    : Effect.void
+                  return event.pipe(
+                    Effect.andThen(
+                      status.set(ctx.sessionID, {
+                        type: "retry",
+                        attempt: info.attempt,
+                        message: info.message,
+                        action: info.action,
+                        next: info.next,
+                      }),
+                    ),
+                  )
                 },
               }),
             ),
@@ -788,6 +821,7 @@ export const defaultLayer = Layer.suspend(() =>
     Layer.provide(Image.defaultLayer),
     Layer.provide(Bus.layer),
     Layer.provide(Config.defaultLayer),
+    Layer.provide(SyncEvent.defaultLayer),
   ),
 )
 
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index 521bacbc2f..934427f569 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -54,7 +54,7 @@ import { InstanceState } from "@/effect/instance-state"
 import { TaskTool, type TaskPromptOps } from "@/tool/task"
 import { SessionRunState } from "./run-state"
 import { EffectBridge } from "@/effect/bridge"
-import { EventV2 } from "@/v2/event"
+import { SyncEvent } from "@/sync"
 import { SessionEvent } from "@/v2/session-event"
 import { Modelv2 } from "@/v2/model"
 import { AgentAttachment, FileAttachment, Source } from "@/v2/session-prompt"
@@ -118,6 +118,7 @@ export const layer = Layer.effect(
     const summary = yield* SessionSummary.Service
     const sys = yield* SystemPrompt.Service
     const llm = yield* LLM.Service
+    const sync = yield* SyncEvent.Service
     const runner = Effect.fn("SessionPrompt.runner")(function* () {
       return yield* EffectBridge.make()
     })
@@ -809,12 +810,14 @@ NOTE: At any point in time through this workflow you should feel free to ask the
               },
             }
             yield* sessions.updatePart(part)
-            EventV2.run(SessionEvent.Shell.Started.Sync, {
-              sessionID: input.sessionID,
-              timestamp: DateTime.makeUnsafe(started),
-              callID,
-              command: input.command,
-            })
+            if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+              yield* sync.run(SessionEvent.Shell.Started.Sync, {
+                sessionID: input.sessionID,
+                timestamp: DateTime.makeUnsafe(started),
+                callID,
+                command: input.command,
+              })
+            }
             return { msg, part, cwd: ctx.directory }
           }).pipe(Effect.ensuring(markReady))
 
@@ -830,12 +833,14 @@ NOTE: At any point in time through this workflow you should feel free to ask the
                 output += "\n\n" + ["<metadata>", "User aborted the command", "</metadata>"].join("\n")
               }
               const completed = Date.now()
-              EventV2.run(SessionEvent.Shell.Ended.Sync, {
-                sessionID: input.sessionID,
-                timestamp: DateTime.makeUnsafe(completed),
-                callID: part.callID,
-                output,
-              })
+              if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+                yield* sync.run(SessionEvent.Shell.Ended.Sync, {
+                  sessionID: input.sessionID,
+                  timestamp: DateTime.makeUnsafe(completed),
+                  callID: part.callID,
+                  output,
+                })
+              }
               if (!msg.time.completed) {
                 msg.time.completed = completed
                 yield* sessions.updateMessage(msg)
@@ -975,34 +980,26 @@ NOTE: At any point in time through this workflow you should feel free to ask the
       }
 
       if (current?.agent !== info.agent) {
-        EventV2.run(
-          SessionEvent.AgentSwitched.Sync,
-          {
-            sessionID: input.sessionID,
-            timestamp: DateTime.makeUnsafe(info.time.created),
-            agent: info.agent,
-          },
-          { bypassExperimentalEventSystem: true },
-        )
+        yield* sync.run(SessionEvent.AgentSwitched.Sync, {
+          sessionID: input.sessionID,
+          timestamp: DateTime.makeUnsafe(info.time.created),
+          agent: info.agent,
+        })
       }
       if (
         current?.model?.providerID !== info.model.providerID ||
         current.model.id !== info.model.modelID ||
         (current.model.variant === "default" ? undefined : current.model.variant) !== info.model.variant
       ) {
-        EventV2.run(
-          SessionEvent.ModelSwitched.Sync,
-          {
-            sessionID: input.sessionID,
-            timestamp: DateTime.makeUnsafe(info.time.created),
-            model: {
-              id: Modelv2.ID.make(info.model.modelID),
-              providerID: Modelv2.ProviderID.make(info.model.providerID),
-              variant: Modelv2.VariantID.make(info.model.variant ?? "default"),
-            },
+        yield* sync.run(SessionEvent.ModelSwitched.Sync, {
+          sessionID: input.sessionID,
+          timestamp: DateTime.makeUnsafe(info.time.created),
+          model: {
+            id: Modelv2.ID.make(info.model.modelID),
+            providerID: Modelv2.ProviderID.make(info.model.providerID),
+            variant: Modelv2.VariantID.make(info.model.variant ?? "default"),
           },
-          { bypassExperimentalEventSystem: true },
-        )
+        })
       }
 
       yield* Effect.addFinalizer(() => instruction.clear(info.id))
@@ -1371,23 +1368,27 @@ NOTE: At any point in time through this workflow you should feel free to ask the
         },
       )
       // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-      EventV2.run(SessionEvent.Prompted.Sync, {
-        sessionID: input.sessionID,
-        timestamp: DateTime.makeUnsafe(info.time.created),
-        prompt: {
-          text: nextPrompt.text.join("\n"),
-          files: nextPrompt.files,
-          agents: nextPrompt.agents,
-        },
-      })
-      for (const text of nextPrompt.synthetic) {
-        // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
-        EventV2.run(SessionEvent.Synthetic.Sync, {
+      if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+        yield* sync.run(SessionEvent.Prompted.Sync, {
           sessionID: input.sessionID,
           timestamp: DateTime.makeUnsafe(info.time.created),
-          text,
+          prompt: {
+            text: nextPrompt.text.join("\n"),
+            files: nextPrompt.files,
+            agents: nextPrompt.agents,
+          },
         })
       }
+      for (const text of nextPrompt.synthetic) {
+        // TODO(v2): Temporary dual-write while migrating session messages to v2 events.
+        if (Flag.OPENCODE_EXPERIMENTAL_EVENT_SYSTEM) {
+          yield* sync.run(SessionEvent.Synthetic.Sync, {
+            sessionID: input.sessionID,
+            timestamp: DateTime.makeUnsafe(info.time.created),
+            text,
+          })
+        }
+      }
 
       return { info, parts }
     }, Effect.scoped)
@@ -1820,6 +1821,7 @@ export const defaultLayer = Layer.suspend(() =>
         LLM.defaultLayer,
         Bus.layer,
         CrossSpawnSpawner.defaultLayer,
+        SyncEvent.defaultLayer,
       ),
     ),
   ),
diff --git a/packages/opencode/src/v2/session.ts b/packages/opencode/src/v2/session.ts
index 39deabfc7c..3b0b61dcbc 100644
--- a/packages/opencode/src/v2/session.ts
+++ b/packages/opencode/src/v2/session.ts
@@ -12,6 +12,7 @@ import { SessionEvent } from "./session-event"
 import { V2Schema } from "./schema"
 import { optionalOmitUndefined } from "@opencode-ai/core/schema"
 import { Modelv2 } from "./model"
+import { SyncEvent } from "@/sync"
 
 export const Delivery = Schema.Literals(["immediate", "deferred"]).annotate({
   identifier: "Session.Delivery",
@@ -113,6 +114,7 @@ export class Service extends Context.Service<Service, Interface>()("@opencode/v2
 export const layer = Layer.effect(
   Service,
   Effect.gen(function* () {
+    const sync = yield* SyncEvent.Service
     const decodeMessage = Schema.decodeUnknownSync(SessionMessage.Message)
 
     const decode = (row: typeof SessionMessageTable.$inferSelect) =>
@@ -269,26 +271,18 @@ export const layer = Layer.effect(
       shell: Effect.fn("V2Session.shell")(function* (_input) {}),
       skill: Effect.fn("V2Session.skill")(function* (_input) {}),
       switchAgent: Effect.fn("V2Session.switchAgent")(function* (input) {
-        EventV2.run(
-          SessionEvent.AgentSwitched.Sync,
-          {
-            sessionID: input.sessionID,
-            timestamp: DateTime.makeUnsafe(Date.now()),
-            agent: input.agent,
-          },
-          { bypassExperimentalEventSystem: true },
-        )
+        yield* sync.run(SessionEvent.AgentSwitched.Sync, {
+          sessionID: input.sessionID,
+          timestamp: DateTime.makeUnsafe(Date.now()),
+          agent: input.agent,
+        })
       }),
       switchModel: Effect.fn("V2Session.switchModel")(function* (input) {
-        EventV2.run(
-          SessionEvent.ModelSwitched.Sync,
-          {
-            sessionID: input.sessionID,
-            timestamp: DateTime.makeUnsafe(Date.now()),
-            model: input.model,
-          },
-          { bypassExperimentalEventSystem: true },
-        )
+        yield* sync.run(SessionEvent.ModelSwitched.Sync, {
+          sessionID: input.sessionID,
+          timestamp: DateTime.makeUnsafe(Date.now()),
+          model: input.model,
+        })
       }),
       subagent: Effect.fn("V2Session.subagent")(function* (input) {
         const parent = yield* result.get(input.parentID)
@@ -319,6 +313,6 @@ export const layer = Layer.effect(
   }),
 )
 
-export const defaultLayer = layer
+export const defaultLayer = layer.pipe(Layer.provide(SyncEvent.defaultLayer))
 
 export * as SessionV2 from "./session"
diff --git a/packages/opencode/test/session/compaction.test.ts b/packages/opencode/test/session/compaction.test.ts
index b48e68b10f..8f987b4d10 100644
--- a/packages/opencode/test/session/compaction.test.ts
+++ b/packages/opencode/test/session/compaction.test.ts
@@ -27,6 +27,7 @@ import { ProviderTest } from "../fake/provider"
 import { testEffect } from "../lib/effect"
 import { CrossSpawnSpawner } from "@opencode-ai/core/cross-spawn-spawner"
 import { TestConfig } from "../fixture/config"
+import { SyncEvent } from "@/sync"
 
 void Log.init({ print: false })
 
@@ -223,6 +224,7 @@ const deps = Layer.mergeAll(
   Plugin.defaultLayer,
   Bus.layer,
   Config.defaultLayer,
+  SyncEvent.defaultLayer,
 )
 
 const env = Layer.mergeAll(
@@ -269,6 +271,7 @@ function compactionProcessLayer(options?: CompactionProcessOptions) {
     Layer.provide(status),
     Layer.provide(bus),
     Layer.provide(options?.config ?? Config.defaultLayer),
+    Layer.provide(SyncEvent.defaultLayer),
   )
 }
 
diff --git a/packages/opencode/test/session/processor-effect.test.ts b/packages/opencode/test/session/processor-effect.test.ts
index a0736b459b..56ff102430 100644
--- a/packages/opencode/test/session/processor-effect.test.ts
+++ b/packages/opencode/test/session/processor-effect.test.ts
@@ -24,6 +24,7 @@ import { CrossSpawnSpawner } from "@opencode-ai/core/cross-spawn-spawner"
 import { provideTmpdirServer } from "../fixture/fixture"
 import { testEffect } from "../lib/effect"
 import { raw, reply, TestLLMServer } from "../lib/llm-server"
+import { SyncEvent } from "@/sync"
 
 void Log.init({ print: false })
 
@@ -166,6 +167,7 @@ const deps = Layer.mergeAll(
   LLM.defaultLayer,
   Provider.defaultLayer,
   status,
+  SyncEvent.defaultLayer,
 ).pipe(Layer.provideMerge(infra))
 const env = Layer.mergeAll(
   TestLLMServer.layer,
diff --git a/packages/opencode/test/session/prompt.test.ts b/packages/opencode/test/session/prompt.test.ts
index 98a69fce96..42c9a81cd2 100644
--- a/packages/opencode/test/session/prompt.test.ts
+++ b/packages/opencode/test/session/prompt.test.ts
@@ -50,6 +50,7 @@ import { Reference } from "../../src/reference/reference"
 import { provideTmpdirInstance, provideTmpdirServer } from "../fixture/fixture"
 import { testEffect } from "../lib/effect"
 import { reply, TestLLMServer } from "../lib/llm-server"
+import { SyncEvent } from "@/sync"
 
 void Log.init({ print: false })
 
@@ -174,6 +175,7 @@ function makeHttp() {
     mcp,
     AppFileSystem.defaultLayer,
     status,
+    SyncEvent.defaultLayer,
   ).pipe(Layer.provideMerge(infra))
   const question = Question.layer.pipe(Layer.provideMerge(deps))
   const todo = Todo.layer.pipe(Layer.provideMerge(deps))
diff --git a/packages/opencode/test/session/snapshot-tool-race.test.ts b/packages/opencode/test/session/snapshot-tool-race.test.ts
index 251a4acf3f..5c47df4c0d 100644
--- a/packages/opencode/test/session/snapshot-tool-race.test.ts
+++ b/packages/opencode/test/session/snapshot-tool-race.test.ts
@@ -58,6 +58,7 @@ import { CrossSpawnSpawner } from "@opencode-ai/core/cross-spawn-spawner"
 import { Ripgrep } from "../../src/file/ripgrep"
 import { Format } from "../../src/format"
 import { Reference } from "../../src/reference/reference"
+import { SyncEvent } from "@/sync"
 
 void Log.init({ print: false })
 
@@ -124,6 +125,7 @@ function makeHttp() {
     mcp,
     AppFileSystem.defaultLayer,
     status,
+    SyncEvent.defaultLayer,
   ).pipe(Layer.provideMerge(infra))
   const question = Question.layer.pipe(Layer.provideMerge(deps))
   const todo = Todo.layer.pipe(Layer.provideMerge(deps))