fix(vertex-live): bill Gemini Live sessions end to end

[marty-sullivan]

TLDR

Problem this solves:

• Live sessions named by alias logged as "unknown", billed nothing
• Grounded Live prompts never carried Google's per-query fee
• The counter died in the Responses usage bridge
• turn_detection: null killed a session with no traceback

How it solves it:

• Resolve the setup model before logging reads it
• Count grounding from the server frames on both Live surfaces
• Carry the counters through the usage bridge both directions
• Guard the null the neighbouring branch already guards

User Flow

Before: a developer running a grounded Gemini Live session sees the session in their logs at a fraction of what Google charged them, and a session addressed by model alias shows up with no model at all

1. They open a WebSocket to wss://litellm-domain/vertex_ai/live and send a setup frame naming gemini-live-2.5-flash-native-audio, the alias their gateway serves
2. They ask a question that needs a web search, attaching the googleSearch tool, and get a spoken answer that cites current information
3. They open https://litellm-domain/ui/?page=logs and the session shows model unknown at $0.00, so neither the tokens nor the search they were just billed for appear anywhere
4. They retry naming the full projects/.../models/gemini-live-2.5-flash-native-audio path instead. Now the model and tokens appear, at $0.00111350, but the grounded search is still free
5. Their Google bill charges $0.035 for that search, so the gateway understates the session roughly thirty fold

After: the same session is logged under its real model with the search charged

1. They open a WebSocket to wss://litellm-domain/vertex_ai/live and send a setup frame naming gemini-live-2.5-flash-native-audio
2. They ask the same question with the same googleSearch tool and get the same spoken answer
3. https://litellm-domain/ui/?page=logs shows the session under gemini-live-2.5-flash-native-audio at $0.03726550, which is $0.00226550 of tokens plus the $0.035 search
4. Running the same session without the tool shows $0.00111350 and no search charge, so the difference is exactly the query fee
5. A client that sends "turn_detection": null now gets a working session rather than a socket that closes with nothing logged

Relevant issues

Linear ticket

Resolves LIT-5846

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• I have added meaningful tests
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Screenshots / Proof of Fix

Shared setup. A deployment serving Gemini Live on Vertex AI, with the group named as an alias:

model_list:
  - model_name: gemini-live-2.5-flash-native-audio
    litellm_params:
      model: vertex_ai/gemini-live-2.5-flash-native-audio
      vertex_project: <project>
      vertex_location: global
      vertex_credentials: /path/to/sa.json

Both cases open wss://<proxy>/vertex_ai/live, send {"setup": {"model": "gemini-live-2.5-flash-native-audio", "generationConfig": {"responseModalities": ["AUDIO"]}}}, then one turn asking a question that needs a search. The grounded case adds "tools": [{"googleSearch": {}}] to the setup frame. Spend is read from GET /spend/logs/v2 afterwards.

Note the native-audio model is the one verified here, and it requires AUDIO in responseModalities; it closes the socket on a TEXT request.

Before (94e0e6e)

grounded session

1. Run the session. The model answers with current information, and the server frames carry groundingMetadata with one webSearchQueries entry
2. Read the spend row: model is unknown, prompt_tokens 0, completion_tokens 0, spend 0.00000000, and cost_breakdown is null
3. Nothing about the session is billed, tokens included

ungrounded control

1. Run the same session with no tools. The model answers normally
2. Read the spend row: model is unknown, spend 0.00000000
3. The two sessions are indistinguishable in the logs

After (8540d65)

grounded session

1. Run the session. Same answer, same groundingMetadata with one query
2. Read the spend row: model is gemini-live-2.5-flash-native-audio, prompt_tokens 19, completion_tokens 188
3. cost_breakdown reads input_cost 0.00000950, output_cost 0.00225600, tool_usage_cost 0.03500000, and spend 0.03726550, which is the three components summed exactly
4. The 0.035 is Google's $35 per 1,000 grounded prompts for this 2.5-era model

ungrounded control

1. Run the same session with no tools
2. Read the spend row: prompt_tokens 19, completion_tokens 92, tool_usage_cost 0.00000000, spend 0.00111350, again summing exactly
3. The only difference between the two rows is the query fee, so nothing else moved

Type

🐛 Bug Fix

Caveats (if any)

Medium

• Grounding counters read the server frames, not usageMetadata
• Vertex reports no grounding count of its own

Low

• web_search_requests reads null in the spend row's detail fields
• The charge is correct; the row's details are lossy already
• Maps grounding is counted, and priced only where a rate exists

Final Attestation

• The tests check the right things, including the edge cases, and regressions in the respective real-world customer use-cases are not possible after this PR

---

Note

Medium Risk
Changes affect proxy spend logging and cost calculation for Live sessions (multi-turn sums, modality inference, grounding fees); incorrect logic would over- or under-charge customers, though behavior is heavily regression-tested.

Overview
Fixes under-billing and missing model attribution for Vertex/Gemini Live WebSocket sessions by aligning usage extraction with how Google reports Live turns and grounding.

Vertex Live passthrough logging now sums usageMetadata across every turn (per-turn context-window billing), aggregates modality breakdowns (including inferring counts when Live omits tokenCount on a lone modality row), builds a full Usage with per-modality details, and reads serverContent.groundingMetadata for web search / Maps query fees. The handler drops its bespoke _calculate_live_api_cost and relies on the shared completion_cost path via the enriched usage object.

Gemini realtime response.done applies the same grounding counter logic from server frames, and the Responses usage bridge forwards web_search_requests and google_maps_grounding_requests so realtime sessions can charge grounding fees.

WebSocket passthrough resolves the setup model alias through the rewriter before extraction, so gateway aliases log a real model instead of unknown at $0.

turn_detection: null is ignored like other optional session fields, avoiding session teardown.

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[marty-sullivan]

@greptileai

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
litellm/llms/gemini/realtime/transformation.py	90.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[greptile-apps]

Greptile Summary

The PR resolves Vertex Live model aliases before logging and preserves modality, grounding, and tool-use usage through billing bridges

• Aggregates usage snapshots and modality details across session turns
• Counts Search and Maps grounding metadata for passthrough and realtime surfaces
• Preserves grounding counters through Responses usage conversions
• Ignores null turn-detection settings instead of attempting to map them

Confidence Score: 5/5

The PR appears safe to merge

No blocking failure remains

Important Files Changed

Filename	Overview
litellm/llms/gemini/realtime/transformation.py	Adds null turn-detection handling and attaches grounding counters to realtime response usage
litellm/proxy/pass_through_endpoints/llm_provider_handlers/vertex_ai_live_passthrough_logging_handler.py	Reworks session usage aggregation and modality-aware billing data while leaving a non-blocking source-comment convention issue
litellm/proxy/pass_through_endpoints/pass_through_endpoints.py	Resolves Vertex Live setup aliases before extracting the model used for logging
litellm/responses/litellm_completion_transformation/transformation.py	Preserves grounding request counters when converting chat usage into Responses usage
litellm/responses/utils.py	Restores grounding counters when converting Responses usage back into chat usage
tests/pass_through_unit_tests/test_vertex_ai_live_passthrough.py	Adds broad billing regressions for multi-turn and grounded sessions
tests/test_litellm/llms/gemini/realtime/test_gemini_realtime_transformation.py	Tests grounding counters through the emitted realtime response event without class-attribute monkeypatching
tests/test_litellm/proxy/pass_through_endpoints/test_pass_through_endpoints.py	Tests alias resolution through the WebSocket relay and logging object

_{Reviews (14): Last reviewed commit: "test(gemini-live): assert grounding coun..." | Re-trigger Greptile}

[marty-sullivan]

@greptileai

[codspeed]

Merging this PR will not alter performance

✅ 31 untouched benchmarks

---

_{Comparing cu-aaii:litellm_vertex_live_passthrough_cost (228d87d) with litellm_internal_staging (ee7c7e1)}

[marty-sullivan]

@greptileai

[veria-ai]

PR overview

All previously flagged issues have been addressed. No open security concerns remain on this pull request.

Security review

No open security issues remain on this pull request.

Fixed/addressed: 2 · PR risk: 0/10

[marty-sullivan]

Holding this: our probe suggests usageMetadata is cumulative, so summing over-bills multi-turn audio ~1.5x. Reworking to last-wins before review

[marty-sullivan]

Retracting this: Google bills Live context per turn, so summing is correct. Our cumulative reading was wrong. Upstream's += stands; the rework is dropped.

[marty-sullivan]

@greptileai reworked: summing restored since Google bills Live context per turn. Body has a fresh three-modality capture at the new tip.

[marty-sullivan]

@greptileai both findings addressed: no Any left in the handler, and tool-use tokens now sum across turns instead of taking the first frame

[marty-sullivan]

@greptileai typed the four session helpers and the turn fixture. Left the pytest fixture params alone, since that file has never annotated them

[marty-sullivan]

@greptileai please re-review. Three commits now cover Live billing end to end: model resolution, grounding counters, and the Responses usage bridge

[marty-sullivan]

@greptileai dropped the call-site comment that restated the helper's docstring, which was your only remaining finding here

[greptile-apps]

Thanks — removing the redundant call-site comment resolves my remaining finding. No further concerns.

[marty-sullivan]

@greptileai please re-review. Rebased onto current staging to clear the merge conflict; the only resolution was a keep-both import collision in one test file.

[marty-sullivan]

@greptileai please re-review. One line collapsed to satisfy ruff format after the rebase; no behavior change.

[marty-sullivan]

@greptileai please re-review. Replaced the patch.object spy with an assertion on the emitted response.done event, which also covers the usage bridge.

[mateo-berri]

@greptileai

[mateo-berri]

bugbot run

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[cursor]

Multi-turn grounding billed once

Medium Severity

All session groundingMetadata is folded into one Usage on a single ModelResponse. The shared search SKU bills per_prompt, so any grounded turn after the first is free even when web_search_requests is greater than one. A multi-turn Live session therefore understates Google's per-prompt grounding fee.

Additional Locations (1)

• litellm/proxy/pass_through_endpoints/llm_provider_handlers/vertex_ai_live_passthrough_logging_handler.py#L293-L298

 

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[mateo-berri]

Thanks for the contribution! I couldn't push the review fixes to your org-owned fork, so this merged as #40915 with your commits kept, merge commit 3ed6c19