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Changelog monitors will miss Perplexity's September 27 Sonar retirement
Perplexity retires its Sonar API on September 27, a date posted in its blog and docs banner but absent from the changelog its FAQ says to watch. Appsmith's managed AI plugin shuts down three days later, on September 30, with no transfer path for uploaded files.
The Engineer · Build desk
What happened
- Perplexity said in an August 13 blog post that the Agent API becomes the main surface on September 27, 2026, and Sonar tiers retire the same day.
- Perplexity's migration guide still says Sonar "remains supported," and its changelog files the Sonar item under July 2026 with no date.
- The replacement is the Agent API at /v1/agent, generally available since February 2026, with the four Sonar presets mapped one to one onto new ones.
- Since Appsmith release 2.3, the API rejects new Appsmith AI datasources and queries with a 400 error, AE-DTS-4031, and existing ones work until September 30.
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Why it matters
- exposure Apps that display Sonar citations are the most likely to break unnoticed after migration, because the UI keeps rendering while the sources come back wrong or empty.
- cost Budget alerts tuned to Sonar token prices will misfire; if each of an xhigh query's 100 steps were one web_search call, tool fees alone would add $0.25 per query.
- constraint Capacity plans that assume more spend buys more throughput stop working at Tier 4: Tier 5 costs $4,000 more in cumulative spend for the same 33 queries per second.
- decision Appsmith apps that depend on uploaded file context have to re-upload or be redesigned before September 30, because the files will not carry over.
Perplexity's FAQ tells customers to watch the changelog for retirements, according to a triage post on dev.to [4]. A team that does exactly that has one undated July entry to schedule against [3]. The 45 days between the August 13 post and the cutoff [1] played out on the blog and a docs banner instead [3]. After September 27, Sonar calls stop working unless the code changes [2]. The post's author wrote: "If your vendor monitoring diffs changelogs, this deadline is invisible to it." [5]
The code change is bigger than a model string. The endpoint path, the request body and the response parsing all change [7]. sonar-pro has a 200K input window, the largest in the Sonar lineup [11]. Perplexity has not published a context-window figure for the Agent API, only per-preset max output tokens [11]. The post advises getting that number from Perplexity in writing before sizing the migration [11].
Two groups fall outside the cutoff. The Search API is a separate product with no deprecation notice, and customers with existing contractual commitments to Sonar are covered through the end of their current term [12].
Appsmith did the unglamorous part of a deprecation well. Besides refusing new work at the API, it puts a deprecation banner with the date on existing datasources and queries, and users cannot dismiss it [13]. The deadline is in the running product, in front of the people who build on it. The hard stop does not wait on upgrades. Appsmith-owned managed credentials are revoked about 60 days after GA, even on instances that upgrade late [14]. The way out is BYOK: move to the OpenAI, Anthropic or Google AI datasources with your own API keys [14].
Teams landing on the Anthropic datasource have one more change to handle. The plugins now live-fetch current model lists. Saved Anthropic queries on hand-typed modern models such as claude-sonnet-4-* now get the raw messages-API body in place of the old completion-shaped one [16]. Any widget or JS object bound to a completion field on those queries needs a new binding [16].
What to watch
- A dated Sonar entry in Perplexity's changelog, or an edit to the migration guide's "remains supported" line, before September 27.
- Perplexity publishing an Agent API context-window figure; sonar-pro workloads sized around 200K input cannot be scoped properly until it does.