Perplexity retires Sonar API on September 27 as Appsmith AI plugin shuts down September 30

Two API retirements in one weekend

Developers have only days left to migrate off two AI APIs. According to a post on dev.to published September 25, Perplexity will retire its Sonar API tiers on September 27, 2026, and Appsmith will shut down its managed Appsmith AI plugin on September 30. The post walks through both migrations and the traps each one contains.

Perplexity Sonar retires first

Perplexity announced in an August 13 blog post that its Agent API becomes the main interface on September 27, 2026, and that Sonar tiers retire the same day, the dev.to post reports. The Agent API, generally available since February 2026 at the /v1/agent endpoint, replaces Sonar under a preset mapping: sonar to fast, sonar-pro to low, sonar-reasoning-pro to medium, and sonar-deep-research to high, with an xhigh preset sitting above all four.

The migration is not a model-string swap. The endpoint path, the request body and the response parsing all change, and the post flags source citations as the highest-risk silent break: a UI that renders citations may keep rendering while the underlying data comes back wrong or empty. Teams that parse the citations array in Sonar responses need to rewrite that parsing code, not just swap model names.

One open question is context length. Sonar-pro offered a 200K-token input window, the largest in the Sonar lineup, but Perplexity publishes no context-window figure for the Agent API, only per-preset output token limits, according to the post. It advises teams that depend on that window to get a number in writing before sizing the work. Perplexity's separate Search API is unaffected, and customers with existing contractual commitments to Sonar are covered through the end of their current term.

New costs and rate limits

The Agent API bills tokens plus per-tool-invocation charges, per the dev.to post: $2.50 per 1,000 web_search calls, $0.50 per 1,000 fetch_url calls, and $5 per 1,000 for finance_search and people_search, with step budgets per preset (fast 1, low 5, medium and high 15, xhigh 100). Budget alerts calibrated on Sonar's token-only pricing may misfire as a result.

Rate limits follow cumulative lifetime spend tiers of $0, $50, $250, $500, $1,000 and $5,000, capped at 1, 3, 8, 17, 33 and 33 queries per second. The post highlights the trap: Tier 5 buys exactly the same throughput as Tier 4, so the ceiling stops lifting once cumulative spend passes $1,000.

Appsmith AI follows on September 30

Since Appsmith release 2.3, creating new Appsmith AI datasources or new queries against existing ones is rejected with a 400 error (AE-DTS-4031), according to the dev.to post, which cites the Appsmith pull request behind the change. Existing datasources and queries keep working until September 30 and now display a non-dismissible deprecation banner carrying the date.

The migration path is bring-your-own-key: move to Appsmith's OpenAI, Anthropic or Google AI datasources with your own API keys. Appsmith-owned managed credentials are revoked roughly 60 days after general availability, which acts as the hard stop even for instances that upgrade late.

Two additional traps stand out. Uploaded files used as file context in Appsmith AI queries will not be available after the shutdown date, with no transfer path, so they must be re-uploaded against the new datasource or the feature redesigned. Separately, a recent Appsmith change that makes datasource plugins live-fetch current model lists means saved Anthropic queries using hand-typed modern model names now receive raw messages-API bodies instead of the older completion-shaped bodies, breaking any widget or JS object still bound to a completion field.

A badly signalled deadline

The sharpest warning in the dev.to post concerns discoverability. The September 27 date appears in Perplexity's blog post and a docs warning banner, but not in the migration guide, which still says Sonar "remains supported", and not as a dated entry in the changelog, where the Sonar item is filed under July 2026 with no date attached. Perplexity's own FAQ directs users to the changelog for retirement notices, so a team following that instruction exactly would never find this deadline. Monitoring tooling that diffs changelogs would miss it as well.

Why it matters

Two API retirements landing within three days of each other compress genuinely different migration work — response parsing, citation handling, cost-model changes and credential management — into a single week. The Perplexity case is also a lesson in how a deprecation can be published yet effectively invisible: when the retirement date never reaches the changelog the vendor's own documentation points to, both automated monitoring and careful teams can miss it. Anyone with Sonar calls or Appsmith AI datasources in production should audit their code and workspaces now; the dev.to author estimates a standard Sonar migration at roughly a day once the parsing changes are scoped, while sonar-pro's 200K context dependency remains an open question to settle with Perplexity first.