Agent and Harness Efficiency
Medium impactLive published free itemCodex CLI 0.153 adds three-tier context management and a token budget mode
Three-tier context management, an experimental token-budget mode, and Guardian history fencing. The third Codex release in a fortnight to target context spend.
What changed
Codex CLI v0.153.0 introduces three-tier context management, an experimental token-budget mode and Guardian history fencing. It follows v0.151.0, which added MCP extension middleware, configurable grace periods and subagent budget accounting so nested workers count against the root goal.
Why it matters
Subagent budget accounting is the significant one. Uncounted nested workers are the classic way an agent run costs several times what the operator expected, because each child looks cheap in isolation. Making children count against a root budget turns agent spend into something you can cap rather than something you discover afterwards.
Take
Three-tier context management, an experimental token-budget mode, and Guardian history fencing. The third Codex release in a fortnight to target context spend.
What to do
If you run Codex with subagents, set a root budget and watch one real task against it before trusting the default. Token-budget mode is experimental, so treat its numbers as directional until you have checked them against your own billing.
Evidence
No public sources are linked yet.