Sterlite Technologies (NSE: STLTECH) hit its 5% upper circuit for a third straight session on Tuesday, at ₹825.60 against Monday's close of ₹787.65 — a fresh 52-week high, on a market cap of about ₹42,500 crore (Business Today, 11:49 AM IST). An upper circuit means the exchange won't let the price rise further that day; buy orders simply sit unfilled. Three in a row means demand kept outrunning the cap.

The stock is up 707% in 2026 and 356% in six months. Off its January low of ₹84.65 it had gained 786% as of 4 September (Business Standard).

What set it off

On 4 September STL put out a three-year plan it calls Lakshya: revenue of ₹20,000 crore by FY29 against ₹4,750 crore in FY26, with EBITDA margin going from 13% to above 27%. Funding it: ₹3,000 crore of capex — about ₹1,000 crore a year — for roughly 50% more preform, fibre and cable capacity, plus a greenfield plant for pre-terminated connectivity.

Tuesday's leg had a second push. Nuvama raised its FY27 and FY28 EBITDA estimates by 22% and 38% on the back of that roadmap (Business Today). A guidance number is a promise; a broker moving its own numbers is someone putting a model behind it. That's what turned a two-day pop into a third circuit.

Why anyone believes it

The order book. It stood at ₹18,600 crore in Q1FY27, up 281% year on year, boosted by a $1.1 billion order from a US hyperscaler. STL's own framing: India's data-centre capacity going from 1.5 GW in 2025 to 10 GW by 2030.

The mechanism is simple. AI training clusters need enormous fibre — inside the building between racks, and between buildings on data-centre interconnect. That's cable by the kilometre, and it's a different customer from a telco rolling out broadband: hyperscalers order in bulk, on schedule, and pay on time. STL makes the glass preform, draws the fibre and jackets the cable itself, which is why it can quote low and still hold margin.

Is it expensive?

Very. STL trades at a P/E of about 180 and 17.8 times book, on last year's return on equity of 1.24% and a three-year average ROE of −2.74% (Screener.in). A 180 P/E on a company that barely earned its cost of capital is not pricing the business as it is — it's pricing FY29 as though it's already delivered.

Put the target itself against the price. ₹20,000 crore at 27% is ₹5,400 crore of EBITDA; the current ₹42,500 crore market cap is roughly 8 times that. On the FY26 base — ₹4,750 crore at 13%, so about ₹618 crore — the same market cap is nearly 69 times. The gap between those two multiples is the bet.

The nearest listed comparison is HFCL, India's other big optical-fibre-cable maker, at a P/E of 65, 7.6 times book and 6.95% ROE on a ₹37,202 crore market cap (Screener.in). Similar size, similar end-market, less than half the multiple and better current returns. Not a call on either — just the price of the same theme, two ways.

The business

STL is India's largest optical fibre and fibre-cable maker with about 8% of the global ex-China OFC market. Three parts: optical fibre and cable (the core), power transmission cables (added in 2006), and STL Digital, its services arm. Q4FY26 came in at ₹1,910 crore of sales and ₹197 crore net profit. The AI-data-centre order is real, but it lands in one segment — this is not a pure-play data-centre stock.

The risk that flips it

Execution arithmetic. Getting from ₹4,750 crore to ₹20,000 crore in three years needs about 61% revenue growth every year, while doubling margin, while spending ₹3,000 crore against ₹1,942 crore of existing borrowings (Screener.in, Mar 2026). Fibre is a capacity business — everyone expands into the same boom, and the last India OFC cycle ended in price cuts. One quarter that misses the run-rate resets a 180 P/E fast. RSI is at 74.5, above the 70 line, and circuit-locked stocks fall the same way they rise: with no buyers on the other side.

As of 8 Sep 2026, ~1:30 PM IST. Prices, targets and order-book figures as reported by the sources cited; valuation ratios as reported by Screener.in. Sources: Business Today, Business Today (FY29 targets), Business Standard, Screener.in (STLTECH), Screener.in (HFCL). For discussion and education only — not investment advice. Verify before acting.