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docs: document FastAPI 0.137 regression and fix in 6.26.2 #2693

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document FastAPI 0.137 regression and fix in 6.26.2
alexandra5000 Jun 23, 2026
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4 changes: 4 additions & 0 deletions docs/reference/supported-technologies.md
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Expand Up @@ -111,6 +111,10 @@ We support these Starlette versions:

Any FastAPI version which uses a supported Starlette version should also be supported.

::::{note}
`fastapi>=0.137` requires `elastic-apm>=6.26.2`.
::::


### GRPC [supported-grpc]

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14 changes: 13 additions & 1 deletion docs/release-notes/known-issues.md
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Expand Up @@ -26,4 +26,16 @@ Known issues are significant defects or limitations that may impact your impleme

:::

_No known issues_
:::{dropdown} FastAPI 0.137+ causes 500 errors on every request
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**Details**
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On 06/19/2026, a known issue was discovered that FastAPI 0.137 changed how included routers are represented internally, introducing `_IncludedRouter` wrapper objects that do not expose a `.path` attribute. The ElasticAPM Starlette/FastAPI middleware accessed `.path` unconditionally, causing an `AttributeError` and a 500 response on every HTTP request when using `app.include_router()`.

**Workaround**
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Pin `fastapi<0.137` until you can upgrade to `elastic-apm>=6.26.2`.

**Resolved**
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On 06/22/2026, this issue was resolved in [{{product.apm-agent-python}} 6.26.2](index.md#elastic-apm-python-agent-6262-release-notes).
:::
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