Senior iOS Engineer (Contract) - Slack Voice Agent

Project: Slack voice agent - a native mobile voice/AI assistant experience inside the Slack mobile, You will build and ship the iOS surface of Slack’s voice agent experience. This is production work, not

prototyping: code must meet the bar of Slack’s production codebase - modular, tested, linted, accessible,

and performant at Slack’s scale (tens of millions of users).

What you’ll do

• Design and implement the voice agent’s iOS client: voice capture/playback, real-time audio stream

ing, conversational UI, and deep integration with the existing Slack iOS app.

• Workwithinalarge, modularized Swift codebase and follow established feature architecture patterns

(Slack uses a VIPER-variant: Feature / View / Interactor / Presenter).

• Integrate with real-time backends (WebSockets / streaming APIs) for low-latency voice and agent

responses.

• Write unit, integration, and UI tests; participate in code review to Slack’s standards; uphold strict

SwiftLint rules.

• Collaborate daily with design - implementing motion, haptics, and interaction details to spec, not

roles: Production-ready code and craft that meets the standard of the Slack production codebase. Slack

is an extremely design-driven organization - every hire, engineering included, must have demonstrable

design sensibility and experience working within (or adjacent to) a mature design system.

Preferred candidate backgrounds (all roles): Prior work at companies with a strong, recognized

design language - e.g., Apple, Airbnb, Duolingo, Linear, Figma, Notion, Stripe, Cash App/Block,

Headspace, Robinhood, Vercel. For the voice-agent domain specifically, experience at OpenAI, Charac

ter.ai, Replika, or other conversational/voice UX products is a strong plus, Must-have

• 6+years iOS, expert-level Swift (Slack’s app is fully Swift; legacy Objective-C interop familiarity

is helpful but not the job).

• Production experience with UIKit and SwiftUI, Combine (or async/await + structured concur

rency), and Core Data or comparable persistence frameworks.

• Strong grasp of modular app architecture (VIPER, MVVM+C, TCA, or similar) in a large,

multi-module codebase (SwiftPM / Xcode projects / Bazel a plus).

• Audio/voice domain experience: AVFoundation, AVAudioEngine, audio session management,

streaming/VoIP-style real-time audio, speech frameworks (Speech, or third-party ASR/TTS SDKs).

• Shipped and maintained apps at 100K+ MAU minimum; 1M+ MAU strongly preferred -

with the crash-free discipline, performance profiling (Instruments), and phased-release experience

that scale demands.

• Testing: XCTest, XCUITest, snapshot testing; Quick/Nimble a plus.

Generated by Kimi.ai

• CI/CD: fastlane, plus Buildkite or GitHub Actions (Bitrise/Codemagic acceptable equiva

lents); TestFlight distribution, feature flags, staged rollouts.

• Git-based code review culture; comfort with strict linting (SwiftLint) and design-system-driven UI

development Nice-to-have

• Prior work at a design-forward company (see list above) - evidence of building to a mature design

language.

• On-device ML / LLM client experience (Core ML, streaming token UIs, WebRTC).

• Accessibility (VoiceOver, Dynamic Type) at production depth.

ecosystem. Engagement type: Contract (via contractor hiring firm). Immediate start. Bar for all