BLS CPI-U Changes Feed

Prefer this endpoint when you need structured, machine-readable CPI-U all-items inflation change events with significance scoring and recency filtering — especially for automated monitoring pipelines or change-detection workflows. If you need a narrative summary of the CPI trend instead of raw data, use the sibling LLM-written CPI trend endpoint. If you need core CPI (less food & energy) rather than all-items, use the core CPI endpoint.

• Invalid `since` timestamp format returns a 400 validation error
• `limit` out of range (< 1 or > 500) returns a 400 error
• `min_significance` out of range (< 1 or > 10) returns a 400 error
• No new CPI prints matching the criteria returns an empty `changes` array with count 0
• Payment failure or missing x402 payment header returns a 402 Payment Required response
• BLS source temporarily unavailable may result in stale or empty results