diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__compact__pre_sampling_model_switch_compaction_shapes.snap.new b/codex-rs/core/tests/suite/snapshots/all__suite__compact__pre_sampling_model_switch_compaction_shapes.snap.new
new file mode 100644
index 0000000000..8d6c4d9b1a
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+++ b/codex-rs/core/tests/suite/snapshots/all__suite__compact__pre_sampling_model_switch_compaction_shapes.snap.new
@@ -0,0 +1,31 @@
+---
+source: core/tests/suite/compact.rs
+assertion_line: 1773
+expression: "format_labeled_requests_snapshot(\"Pre-sampling compaction on model switch to a smaller context window: current behavior compacts using prior-turn history only (incoming user message excluded), and the follow-up request carries compacted history plus the new user message.\",\n&[(\"Initial Request (Previous Model)\", &requests[0]),\n(\"Pre-sampling Compaction Request\", &requests[1]),\n(\"Post-Compaction Follow-up Request (Next Model)\", &requests[2]),])"
+---
+Scenario: Pre-sampling compaction on model switch to a smaller context window: current behavior compacts using prior-turn history only (incoming user message excluded), and the follow-up request carries compacted history plus the new user message.
+
+## Initial Request (Previous Model)
+00:message/developer:<PERMISSIONS_INSTRUCTIONS>
+01:message/user:<AGENTS_MD>
+02:message/user:<ENVIRONMENT_CONTEXT:cwd=<CWD>>
+03:message/developer:<PERMISSIONS_INSTRUCTIONS>
+04:message/user:before switch
+
+## Pre-sampling Compaction Request
+00:message/developer:<PERMISSIONS_INSTRUCTIONS>
+01:message/user:<AGENTS_MD>
+02:message/user:<ENVIRONMENT_CONTEXT:cwd=<CWD>>
+03:message/developer:<PERMISSIONS_INSTRUCTIONS>
+04:message/user:before switch
+05:message/assistant:before switch
+06:message/user:<SUMMARIZATION_PROMPT>
+
+## Post-Compaction Follow-up Request (Next Model)
+00:message/developer:<PERMISSIONS_INSTRUCTIONS>
+01:message/user:<AGENTS_MD>
+02:message/user:<ENVIRONMENT_CONTEXT:cwd=<CWD>>
+03:message/user:before switch
+04:message/user:<COMPACTION_SUMMARY>\nPRE_SAMPLING_SUMMARY
+05:message/developer:<model_switch>\nThe user was previously using a different model....
+06:message/user:after switch