fix: change cost calculation logs from INFO to DEBUG level

[colesmcintosh]

Title

fix: change cost calculation logs from INFO to DEBUG level

Relevant issues

Part 2/2 of fix for #9815

Pre-Submission checklist

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

• I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
• I have added a screenshot of my new test passing locally
• My PR passes all unit tests on make test-unit
• My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🐛 Bug Fix

Changes

This PR changes cost calculation logs from INFO to DEBUG level to reduce log noise in production environments.

Problem

Cost calculation logs ("selected model name for cost calculation") were being emitted at INFO level, which is too verbose for production use. These logs should be debug-level information that's only shown when troubleshooting.

Solution

Changed verbose_logger.info() to verbose_logger.debug() for:

1. Model selection logs in completion_cost() function
2. Batch cost calculation logs in batch_cost_calculator() function

Testing

Added tests in test_cost_calculation_log_level.py that verify:

• Cost calculation logs are emitted at DEBUG level
• Batch cost calculation logs are emitted at DEBUG level

Test Output

tests/test_litellm/test_cost_calculation_log_level.py::test_batch_cost_calculation_uses_debug_level PASSED [ 50%]
tests/test_litellm/test_cost_calculation_log_level.py::test_cost_calculation_uses_debug_level PASSED [100%]
========================= 2 passed, 1 warning in 0.12s =========================

This is part 2 of a 2-part fix. The first PR (#12111) addresses the root cause by making loggers respect the LITELLM_LOG environment variable.

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Name	Status	Preview	Comments	Updated (UTC)
litellm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 27, 2025 5:44pm

[ishaan-jaff]

cc @corbt

[ishaan-jaff]

LGTM

[corbt]

Awesome, thanks!! Excited to see this in a release!