# Cache TTL appears to have silently regressed from 1h to 5m around early March …2026, causing significant quota and cost inflation
## Summary
Analysis of raw Claude Code session JSONL files spanning Jan 11 – Apr 11, 2026 shows that Anthropic appears to have **silently changed the prompt cache TTL default from 1 hour to 5 minutes sometime in early March 2026**. Prior to this change, Claude Code was receiving 1-hour TTL cache writes — which we believe was the intended default. The reversion to 5-minute TTL has caused a **20–32% increase in cache creation costs** and a measurable spike in quota consumption for subscription users who have never previously hit their limits.
This appears directly related to the behavior described in #45756.
---
## Data
Session data extracted from `~/.claude/projects/` JSONL files across **two machines** (Linux workstation + Windows laptop, different accounts/sessions), totaling **119,866 API calls** from Jan 11 – Apr 11, 2026. Each assistant message includes a `usage.cache_creation.ephemeral_5m_input_tokens` / `ephemeral_1h_input_tokens` breakdown that makes the TTL tier per-call observable. Having two independent machines strengthens the signal — both show the same behavioral shift at the same dates.
### Phase breakdown
| Phase | Dates | TTL behavior | Evidence |
|-------|-------|--------------|----------|
| 1 | Jan 11 – Jan 31 | **5m ONLY** | `ephemeral_1h` absent/zero — likely predates 1h tier availability in the API |
| 2 | Feb 1 – Mar 5 | **1h ONLY** | `ephemeral_5m = 0`, `ephemeral_1h > 0` across **33+ consecutive days** on both machines — near-zero exceptions |
| 3 | Mar 6–7 | **Transition** | First 5m tokens re-appear, small volumes, 1h still present |
| 4 | Mar 8 – Apr 11 | **5m dominant** | 5m tokens surge to majority; 1h becomes minority or disappears entirely |
We believe Phase 2 represents Anthropic's **intended default behavior** — 1h TTL was rolled out as the Claude Code standard around Feb 1 and held consistently for over a month across two independent machines on two different accounts. January's all-5m data most likely predates the 1h TTL tier being available in the API. The regression began **around March 6–8, 2026**.
No client-side changes were made between phases. The same Claude Code version and usage patterns were in place throughout. The TTL tier is set server-side by Anthropic.
### Day-by-day TTL data showing the regression (combined, both machines)
```
Date | 5m-create | 1h-create | Behavior
------------|------------|------------|----------
2026-02-01 | 0.00M | 1.70M | 1h ONLY ← 1h default begins
2026-02-09 | 0.00M | 7.95M | 1h ONLY
2026-02-15 | 0.00M | 13.61M | 1h ONLY ← heaviest day, 100% 1h
2026-02-28 | 0.00M | 16.15M | 1h ONLY ← 16M tokens, still 100% 1h
2026-03-01 | 0.00M | 0.12M | 1h ONLY
2026-03-04 | 0.00M | 8.12M | 1h ONLY
2026-03-05 | 0.00M | 6.55M | 1h ONLY ← last clean 1h-only day
| | |
2026-03-06 | 0.29M | 0.22M | MIXED ← first 5m tokens reappear
2026-03-07 | 4.56M | 0.50M | MIXED ← 5m surging
2026-03-08 | 16.86M | 3.44M | MIXED ← 5m now dominant (83%)
2026-03-10 | 10.55M | 0.51M | MIXED
2026-03-15 | 19.47M | 1.84M | MIXED
2026-03-21 | 21.37M | 1.70M | MIXED ← 93% 5m
2026-03-22 | 13.48M | 2.85M | MIXED
```
The transition is visible to the day: **March 6 is when 5m tokens first reappear** after 33 days of clean 1h-only behavior. By March 8, 5m tokens outnumber 1h by 5:1. This is consistent with a server-side configuration change being rolled out gradually then completing around March 8.
---
## Cost impact
Applying official Anthropic pricing (rates.json, updated 2026-04-09):
Combined dataset (119,866 API calls, two machines):
**claude-sonnet-4-6** (`cache_write_5m = $3.75/MTok`, `cache_write_1h = $6.00/MTok`, `cache_read = $0.30/MTok`):
| Month | Calls | Actual cost | Cost with 1h TTL | Overpaid | % waste |
|-------|-------|-------------|-----------------|----------|---------|
| Jan 2026 | 2,639 | $78.99 | $37.54 | $41.45 | **52.5%** |
| Feb 2026 | 27,220 | $1,120.43 | $1,108.11 | $12.32 | **1.1%** ← nearly 0 on 1h |
| Mar 2026 | 68,264 | $2,776.11 | $2,057.01 | $719.09 | **25.9%** |
| Apr 2026 | 21,743 | $1,193.01 | $1,016.78 | $176.23 | **14.8%** |
| **Total** | **119,866** | **$5,561.17** | **$4,612.09** | **$949.08** | **17.1%** |
**claude-opus-4-6** (`cache_write_5m = $6.25/MTok`, `cache_write_1h = $10.00/MTok`, `cache_read = $0.50/MTok`):
| Month | Calls | Actual cost | Cost with 1h TTL | Overpaid | % waste |
|-------|-------|-------------|-----------------|----------|---------|
| Jan 2026 | 2,639 | $131.65 | $62.57 | $69.08 | **52.5%** |
| Feb 2026 | 27,220 | $1,867.38 | $1,846.85 | $20.53 | **1.1%** ← nearly 0 on 1h |
| Mar 2026 | 68,264 | $4,626.84 | $3,428.36 | $1,198.49 | **25.9%** |
| Apr 2026 | 21,743 | $1,988.35 | $1,694.64 | $293.71 | **14.8%** |
| **Total** | **119,866** | **$9,268.97** | **$7,687.17** | **$1,581.80** | **17.1%** |
February — the month Anthropic was defaulting to 1h TTL — shows only **1.1% waste** (trace 5m activity from one machine on one day). Every other month shows 15–53% overpayment from 5m cache re-creations. The cost difference is explained entirely by TTL tier, not by usage volume. The **percentage waste is identical across model tiers** (17.1%) because it is driven purely by the 5m/1h token split, not by per-token price.
### Why 5m TTL is so expensive in practice
With 5m TTL, any pause in a session longer than 5 minutes causes the entire cached context to expire. On the next turn, Claude Code must re-upload that context as a fresh `cache_creation` at the write rate, rather than a `cache_read` at the read rate. The write rate is **12.5× more expensive** than the read rate for Sonnet, and the same ratio holds for Opus.
For long coding sessions — which are the primary Claude Code use case — this creates a compounding penalty: the longer and more complex your session, the more context you have cached, and the more expensive each cache expiry becomes.
Over the 3-month period analyzed:
- **220M tokens** were written to the 5m tier
- Those same tokens generated **5.7B cache reads** — meaning they were actively being used
- Had those 220M tokens been on the 1h tier, re-accesses within the same hour would be reads (~$0.30–0.50/MTok) instead of re-creations (~$3.75–6.25/MTok)
---
## Quota impact
Users on Pro/subscription plans are quota-limited, not just cost-limited. Cache creation tokens count toward quota at full rate; cache reads are significantly cheaper (the exact coefficient is under investigation in #45756). The silent reversion to 5m TTL in March is the most likely explanation for why subscription users began hitting their 5-hour quota limits for the first time — including the author of this issue, who had never hit quota limits before March 2026.
---
## Hypothesis
The data strongly suggests that **1h TTL was the intended default for Claude Code** and was in place as of early February 2026. Sometime between Feb 27 and Mar 8, 2026, Anthropic silently changed the default to 5m TTL — either intentionally as a cost-saving measure, or accidentally as an infrastructure regression.
Evidence supporting "1h was the intended default":
- Phase 2 (1h ONLY) shows *zero* 5m tokens across **14 separate active days** spanning 3+ weeks — this is not noise or partial rollout, it is consistent deliberate behavior
- The February cost profile is the only month with 0% overpayment — it represents what users should have been paying all along
- The March reversion immediately produced the largest 5m-tier days in the entire dataset (30M tokens on Mar 22 alone), suggesting a sudden configuration flip rather than gradual drift
- Subscription users began hitting 5-hour quota limits **for the first time** in March — directly coinciding with the reversion
The most likely sequence of events:
1. **~Feb 1 and prior**: Anthropic defaulted to 1h TTL for Claude Code subscription users
2. **~Mar 6**: 5m tokens begin reappearing — gradual rollout of the change or partial infrastructure flip
3. **~Mar 8**: 5m TTL becomes dominant — the regression is fully in effect across both tested machines and accounts
4. **Mar 8+**: Mixed behavior continues, suggesting either incomplete rollout, A/B testing, or regional infrastructure variance
The 33-day window of clean 1h-only behavior (Feb 1 – Mar 5) across two independent machines and two separate accounts makes this one of the strongest available signals that **1h TTL was Anthropic's deliberate default**, not a fluke.
---
## Request
1. **Confirm or deny** whether Anthropic made a server-side TTL default change in early February 2026 and reverted it in early March 2026
2. **Clarify the intended TTL behavior** for claude-code sessions — is 5m the intended default, or was 1h intended to be permanent?
3. **Consider restoring 1h TTL as the default** for Claude Code sessions, or exposing it as a user-configurable option. The 5m TTL is disproportionately punishing for the long-session, high-context use case that defines Claude Code usage
4. **Disclose quota counting behavior for cache_read tokens** (ref #45756) so users can make informed decisions about their usage patterns
---
## Methodology
- Source: raw `~/.claude/projects/**/*.jsonl` session files (Claude Code stores per-message API responses including full `usage` objects)
- Extraction: filtered for `type: "assistant"` entries with `message.usage.cache_creation` field
- No external tools or proxies involved — this data comes directly from Claude Code's own session logs
- Analysis tool: [cnighswonger/claude-code-cache-fix](https://github.com/cnighswonger/claude-code-cache-fix) `quota-analysis --source` mode (added to support this investigation)
- Pricing: official Anthropic rates from `rates.json` (updated 2026-04-09)
这就是4.6这几天仿佛傻子的原因吗，充满了幻觉，臆想，也不听指令，说了不要用memory要去找文献，完全不听…