fix: route api.anthropic.com custom providers through anthropic_messages on fallback by x9x9x9x9x9x91 · Pull Request #49247 · NousResearch/hermes-agent

x9x9x9x9x9x91 · 2026-06-19T20:19:46Z

Problem

On the fallback provider path, api_mode detection misses custom providers that point at the native Anthropic host (api.anthropic.com) without a /anthropic base-URL suffix.

The fallback resolver only matches:

elif fb_provider == "anthropic" or fb_base_url.rstrip("/").lower().endswith("/anthropic"):
    fb_api_mode = "anthropic_messages"

A custom provider (e.g. one named cron-anthropic) whose base_url is https://api.anthropic.com has neither provider == "anthropic" nor a /anthropic suffix, so it falls through to chat_completions → POST /v1/chat/completions → 404 against the Anthropic host on every fallback.

The primary path already handles this correctly in determine_api_mode() by matching the host. The fallback path just doesn't mirror it.

Fix

Mirror the primary path's host check in the fallback resolver: also route to anthropic_messages when base_url_hostname(fb_base_url) == "api.anthropic.com".

elif (
    fb_provider == "anthropic"
    or fb_base_url.rstrip("/").lower().endswith("/anthropic")
    or base_url_hostname(fb_base_url) == "api.anthropic.com"
):
    fb_api_mode = "anthropic_messages"

Test

Adds tests/run_agent/test_provider_fallback.py covering a custom provider pointed at api.anthropic.com with no /anthropic suffix, asserting it resolves to anthropic_messages on fallback (not chat_completions). Full file: 23 passed.

Fixes the whole class — name match, suffix match, and host match — not just the one site.

…ges on fallback The fallback activation path re-derived api_mode from the provider name and a "/anthropic" URL-suffix check, missing custom providers (e.g. cron-anthropic) that point at the native api.anthropic.com host with no path suffix. They defaulted to chat_completions, so failover POSTed /v1/chat/completions and 404'd on every attempt — the configured Anthropic fallback never actually worked. Match the host the same way the primary path's determine_api_mode() already does. Adds a regression test asserting an api.anthropic.com custom-provider fallback entry resolves to anthropic_messages.

…ction Widen the salvaged #32243 fix to the try_activate_fallback path: a custom provider pointed at the native api.anthropic.com host (no /anthropic path suffix, name != anthropic) fell through to chat_completions -> POST /v1/chat/completions -> 404. Match the host the same way determine_api_mode() and _detect_api_mode_for_url() now do. Absorbs #49247.

Pins that a custom provider on the native api.anthropic.com host resolves to anthropic_messages on the try_activate_fallback path. From #49247.

teknium1 · 2026-07-01T09:19:18Z

Merged via #56214, which fixes the same api.anthropic.com host-detection bug. Your try_activate_fallback fix was absorbed and your test cherry-picked with your authorship preserved (24cb80f). Both you and @xxxigm are credited — thanks for catching the fallback-path sibling site.

…ction Widen the salvaged NousResearch#32243 fix to the try_activate_fallback path: a custom provider pointed at the native api.anthropic.com host (no /anthropic path suffix, name != anthropic) fell through to chat_completions -> POST /v1/chat/completions -> 404. Match the host the same way determine_api_mode() and _detect_api_mode_for_url() now do. Absorbs NousResearch#49247.