Replace deprecated @app.on_event with lifespan context manager - #389
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Qiaochu Hu (hobostay) wants to merge 1 commit into
Open
Replace deprecated @app.on_event with lifespan context manager#389Qiaochu Hu (hobostay) wants to merge 1 commit into
Qiaochu Hu (hobostay) wants to merge 1 commit into
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FastAPI deprecated @app.on_event("startup") since version 0.103.0
and it will be removed in a future release. Replace with the
recommended lifespan context manager pattern.
This also prevents potential issues with auto-reload loading the
model multiple times into GPU memory.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Rick Thomas (rickthomasjr)
approved these changes
Jun 14, 2026
Rick Thomas (rickthomasjr)
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Review: Approve — replace deprecated @app.on_event with lifespan
Correctness: @app.on_event("startup") and @app.on_event("shutdown") are deprecated in FastAPI 0.95+ in favor of the lifespan context manager pattern. This is a forward-compatibility fix.
Changes are correct: The async context manager properly yields between startup (model loading) and shutdown (model cleanup), matching the original semantics exactly.
Verdict: Approve. Non-breaking forward-compat fix.
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Summary
@app.on_event("startup")with the recommendedlifespancontext manager pattern indemo/web/app.py@app.on_event("startup")is deprecated since FastAPI 0.103.0 and will be removed in a future versionDetails
Affected file:
demo/web/app.py(lines 335-356)The deprecated
on_event("startup")pattern has known issues with auto-reload where the startup event may fire multiple times, loading multiple copies of the large model into GPU memory and causing OOM. The lifespan context manager is the recommended replacement.Test plan
MODEL_PATHset and verify it loads correctly🤖 Generated with Claude Code